Method and system for providing a perpendicular magnetic recording transducer using a low energy mill

ABSTRACT

A method and system for fabricating magnetic transducer are described. The method and system include providing a main pole having a bottom and a top wider than the bottom. The method and system further include performing a high energy ion mill at an angle from a normal to the top of the main pole and at a first energy. The high energy ion mill removes a portion of the top of the main pole and exposes a top bevel surface for the main pole. The method and system also include performing a low energy ion mill at second energy and a glancing angle from the top bevel surface. The glancing angle is not more than fifteen degrees. The second energy is less than the first energy. The method and system also include depositing a nonmagnetic gap.

BACKGROUND

FIG. 1 is a flow chart depicting a conventional method 10 forfabricating a conventional perpendicular magnetic recording (PMR)transducer. For simplicity, some steps are omitted. A conventional poleis provided, via step 12. The conventional pole is magnetic and has atop wider than its bottom. Step 12 typically includes depositing on ormore high moment magnetic layers in the desired shape. For example,materials containing Co, Fe, and/or Ni with a high moment may bedeposited in a trench having the desired trapezoidal profile or blanketdeposited and subjected to a photolithographic process to provide thedesired trapezoidal profile. In addition, the conventional pole isdesired to have at least a trailing edge, or top, bevel. Thus, theconventional pole is desired to be shorter in the region of theair-bearing surface (ABS) location. The ABS location is the location atwhich the ABS will reside in the completed structure. In addition to thetrailing edge bevel, the conventional pole may include a leading edgebevel.

To form the bevel, a mask is provided, via step 14. Step 14 may includeproviding bottom antireflective coating (BARC) and other layers as wellas depositing and patterning a hard mask or other mask for bevelformation. A high energy ion mill is performed, via step 16. The ionmill is typically performed at an angle from normal to the surface toprovide a sloped trailing edge bevel. The energy of the ion mill istypically seven hundred eV or greater. A high energy ion mill is desiredin order to remove the pole material at a sufficiently high rate for thedesired throughput in manufacturing processes. For example, the highenergy ion mill may remove on the order of 1600-2000 Angstroms in a fewminutes.

A conventional gap layer is provided, via step 18. Step 18 may include abrief sputter etch followed by deposition of the conventional gap layer.The conventional gap layer is nonmagnetic and may be insulating. Theconventional gap layer is typically alumina deposited using atomic layerdeposition (ALD). As a result, the conventional gap is conformal,covering the top and side of the conventional PMR pole.

Fabrication of the transducer is then completed, via step 20. Forexample, a wrap-around shield, coils, other shield(s) and otherstructures may be fabricated. In addition, the transducer is lapped toexpose the ABS.

FIG. 2 depicts a portion of a conventional PMR transducer 50 formedusing the conventional method 10. The conventional transducer 50includes an underlayer 52, a conventional pole 54 including trailingbevel 56, and a conventional gap 58. Other structures (not shown) arealso fabricated using the conventional method 10.

Although the conventional method 10 may provide the conventional PMRtransducer 50, there may be drawbacks. In particular, the top layer ofthe pole may be damaged. As can be seen in FIG. 2, the pole 56 includesa damaged region 60. This region is generally amorphous instead ofcrystalline. The amorphous damaged region 60 has a lower saturationmagnetic flux density (B_(s)) and lowers the overall B_(s) of theconventional pole 54. A reduction in the B_(s) of the pole isundesirable. Further, the damaged region 60 may result in the effectivethickness of the gap 58 varying. Such a variation in the nonmagnetic gap58 thickness is undesirable. Accordingly, what is needed is an improvedmethod for fabricating a transducer.

SUMMARY

A method and system for fabricating magnetic transducer are described.The method and system include providing a main pole having a bottom anda top wider than the bottom. The method and system further includeperforming a high energy ion mill at an angle from a normal to the topof the main pole and at a first energy. The high energy ion mill removesa portion of the top of the main pole and exposes a top bevel surfacefor the main pole. The method and system also include performing a lowenergy ion mill at second energy and a glancing angle from the top bevelsurface. The glancing angle is not more than fifteen degrees. The secondenergy is less than the first energy. The method and system also includedepositing a nonmagnetic gap.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a flow chart depicting a conventional method for fabricating aPMR transducer.

FIG. 2 is a diagram depicting a conventional PMR transducer.

FIG. 3 is a flow chart depicting an exemplary embodiment of a method forfabricating a PMR transducer.

FIG. 4 is a diagram depicting an exemplary embodiment of a PMRtransducer.

FIG. 5 is a diagram depicting an exemplary embodiment of a PMR headincorporating the PMR transducer.

FIG. 6 is a flow chart depicting another exemplary embodiment of amethod for fabricating a PMR transducer.

FIGS. 7-13 are diagrams depicting an exemplary embodiment of a PMRtransducer during fabrication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a flow chart depicting an exemplary embodiment of a method 100for fabricating a transducer. The method 100 is described in the contextof a PMR transducer, though other transducers might be so fabricated.For simplicity, some steps may be omitted and/or combined. The PMRtransducer being fabricated may be part of a merged head that alsoincludes a read head (not shown) and resides on a slider (not shown) ina disk drive. The method 100 also may commence after formation of otherportions of the PMR transducer. The method 100 is also described in thecontext of providing a main pole and its associated structures in asingle magnetic recording transducer. However, the method 100 may beused to fabricate multiple structures and/or multiple transducers atsubstantially the same time. The method 100 and system are alsodescribed in the context of particular layers. However, in someembodiments, such layers may include multiple sub-layers. In oneembodiment, the method 100 commences after formation of theunderlayer(s) on which the main pole is to reside.

A main pole is provided, via step 102. The main pole may be a PMR pole.Thus, the top of the main pole may be wider than the bottom. In someembodiments, the main pole provided may have a leading edge, or bottombevel. Thus, the region of the main pole at the ABS may be shorter thana portion of the main pole distal from the ABS. Step 102 may beperformed by depositing a layer, providing a trench having the desiredprofile in the layer and depositing the material(s) for the pole in thetrench. Alternatively, the magnetic and other material(s) for the polemay be deposited and a portion of the material(s) removed to form thepole.

A trailing edge, or top bevel, is formed using a high energy ion mill,via step 104. Step 104 may also including providing a mask exposing theportion of the main pole proximate to the ABS location, then ion millingthe exposed portion of the magnetic transducer at a high energy. Theenergy of an ion mill refers to the energy of the ions being used in themilling process. In some embodiments, the high energy is at least fivehundred eV. In some such embodiments, the high energy is at least sevenhundred eV. The high energy ion mill is also performed at a nonzeroangle to normal to the top surface of the main pole. In someembodiments, this angle is at least thirty-five and not more than fiftyfive degrees. In other embodiments, the angle may be at least forty andnot more than fifty degrees. Further, the angle is such that the highenergy ion mill is a back side ion mill. Thus, the ions approach the ABSlocation from the back side of the transducer. The high energy ion millremoves a portion of the main pole and exposes a top bevel surface ofthe main pole. The top bevel surface is sloped at a bevel angle withrespect to the ABS. The bevel angle is nonzero. Further, the high energyion mill may provide a milling rate having a sufficiently high removalrate for a desired throughput. For example, the high energy mightcorrespond to removing 1600-2000 Angstroms from the main pole in a fewminutes. The high energy ion mill may also include a front side ion millthat is used to clean redeposition from the top bevel surface.

A low energy ion mill is performed, via step 106. In some embodiments,this low energy ion mill is performed after removal of the mask used inthe high energy ion mill of step 104. The low energy ion mill is at anenergy that is lower than the high energy ion mill. In some embodiments,the low energy ion mill is at an energy at least three hundred eV lessthan that of the high energy ion mill. For example, in some embodiments,the low energy ion mill may be at an energy of not more than two hundredand fifty eV. In some such embodiments, the low energy ion mill is at anenergy of not more than two hundred eV. Further, in some embodiments,the energy of the low energy ion mill is not greater than one hundredeV. In some embodiments, it may be desired to perform the ion mill ofstep 106 in as low an energy as possible for the tool used while stillmaintaining a stable ion mill. The low energy ion mill is also providedat a glancing angle from the top bevel surface. In some embodiments,this glancing angle is not more than fifteen degrees. In some suchembodiments, the glancing angle is at least ten degrees. In someembodiments, the glancing angle corresponds to an angle with respect tonormal to the top surface of the main pole that is approximately thesame as the high energy ion mill angle. In some embodiments, however,the glancing angle corresponds to an angle respect to normal to the topsurface of the main pole that is different from the high energy ion millangle. For example, the glancing angle may correspond to an angle withrespect to normal to the surface that is greater than the angle of thehigh energy ion mill.

A nonmagnetic gap covering the main pole is provided, via step 108. Atleast a portion of the nonmagnetic gap resides on the top of the mainpole. In some embodiments, step 108 includes performing a sputter cleanto preclean the transducer and then depositing a nonmagnetic layer, suchas alumina, using ALD. Because ALD is used, the nonmagnetic gap may beconformally deposited. Thus, the top and sides of the main pole may becovered by the nonmagnetic gap. Further, the nonmagnetic gap may followthe profile of the main pole. However, in other embodiments, otherdeposition mechanisms, including nonconformal deposition, may be used.In addition, the nonmagnetic gap may cover other structures in thetransducer.

Fabrication of the magnetic transducer may then be completed, via step110. In some embodiments, step 110 includes providing a wrap-aroundshield proximate to the ABS location. Fabrication of the wrap-aroundshield may include depositing seed layers for the wrap-around shield,providing a mask for the wrap-around shield, then electroplating thewrap-around shield. Further, insulating layer(s), coil(s), othershield(s) and/or other structures may be fabricated.

FIG. 4 is a diagram depicting an exemplary embodiment of a portion of aPMR transducer 200 that may be formed using the method 100. FIG. 5depicts a head 250 incorporating the transducer 200′. For clarity, FIGS.4-5 are not to scale. FIG. 4 depicts side and ABS views of thetransducer 200, while FIG. 5 depicts a side view only of the head 250.The head 250 shown includes a read transducer 252 and the PMR transducer200′. However, in another embodiment, the transducer 200/200′ may beused in a head including only one or more write transducers 200/200′.The read transducer 252 includes shields 254 and 258 as well as sensor256. The PMR transducer 200′ shown in FIG. 5 includes poles 260 and 264,shield 268, and coils 262 and 266 in addition to the portion of the PMRtransducer 200 that is also shown in FIG. 4. The PMR transducer 200/200′includes underlayer 202/202′, a main pole 204/204′ having a trailingedge bevel 206/206′, and gap 208/208′. Also shown in FIG. 5 are awrap-around shield 214 and the seed layer 212 for the wrap-aroundshield. Other and/or different components may be fabricated in otherembodiments. Although not shown, the pole 204/204′ might also include abottom, or leading edge bevel. However, in some embodiments, the leadingedge bevel may be omitted. Also shown is the ABS location in FIG. 4 andthe ABS in FIG. 5. For example, in some embodiments, the transducer 200is lapped to expose the surface of the transducer 200 at the ABSlocation.

Using the method 100, main pole 204/204′ having a trailing edge bevel206/206′ may be formed. Further, the damage 210/210′ to the main polemay be reduced. More specifically, the high energy ion mill of step 104may cause the main pole to be damaged, for example forming an amorphouslayer at the top bevel surface 206/206′. Some of the damage 210/210′ isremoved without causing significant additional damage by the low energy,glancing angle ion mill of step 106. After the low energy ion mill ofstep 106, the thickness of the damaged region 210/210′ may be less thantwenty-five Angstroms. For example, the thickness may be on the order ofnineteen through twenty-one Angstroms. In some embodiments, thethickness of the damaged region 210/210′ is less than twenty Angstromsafter the low energy ion mill of step 106. Further, precleaning of themain pole 204/204′ prior to deposition of the gap 208/208′ may furtherreduce the damage to the main pole 204/204′. In some embodiments, thethickness of the damaged/amorphous region 210/210′ may be less thantwenty Angstroms after deposition of the gap 208/208′. In some suchembodiments, the thickness of the damaged region 210/210′ may beapproximately fifteen Angstroms or less. Because the damaged region210/210′ is thinner, reductions in the saturation magnetization of themain pole 204/204′ due to the damaged region 210/210′ maybe ameliorated.Such a higher saturation magnetization is generally desirable in themain pole 204/204′. Further, the thickness of the nonmagnetic gap layer208/208′ may be better controlled. Thus, performance of the transducer200/200′ and head 250 may be improved.

FIG. 6 is a flow chart depicting another exemplary embodiment of amethod 300 for fabricating a transducer, such as a PMR transducer. Forsimplicity, some steps may be omitted. FIGS. 7-13 are diagrams depictingside views of an exemplary embodiment of a portion of a transducer 400during fabrication. For clarity, FIGS. 7-13 are not to scale. Further,although FIGS. 7-13 depict the ABS location at a particular point in thepole, other embodiments may have other locations for the ABS. Structuresin FIGS. 7-13 are shown as terminating at the ABS. During fabrication,at least a portion of such structures typically extend beyond the ABS.The portions of the structures extending beyond the ABS location aregenerally removed later in fabrication, for example by lapping thetransducer 400. However, for simplicity, the transducer 400 is onlyshown as extending to the ABS location. Referring to FIGS. 6-13, themethod 300 is described in the context of the transducer 400. However,the method 300 may be used to form another device (not shown). Thetransducer 400 being fabricated may be part of a merged head that alsoincludes a read head (not shown in FIGS. 7-13) and resides on a slider(not shown) in a disk drive. The method 300 also may commence afterformation of other portions of the transducer 400. The method 300 isalso described in the context of providing a single transducer 400 and asingle pole. However, the method 300 may be used to fabricate multipletransducers and/or multiple poles at substantially the same time. Themethod 300 and device 400 are also described in the context ofparticular layers. However, in some embodiments, such layers may includemultiple sublayers.

A main pole bottom is provided, via step 302. Step 302 is analogous tostep 102 of the method 100. The main pole may be a PMR pole. Thus, thetop of the main pole may be wider than the bottom. In addition, step 102may include forming a leading edge bevel. Thus, the region of the mainpole at the ABS may be shorter than a portion of the main pole distalfrom the ABS. Step 102 may be performed by depositing a layer, providinga trench having the desired profile in the layer and depositing thematerial(s) for the pole in the trench. For example, the polematerial(s) may be electroplated. Alternatively, the magnetic and othermaterial(s) for the pole may be deposited and a portion of thematerial(s) removed to form the pole. The main is generally includespole material(s) that are alloys including Co, Fe, and/or Ni with a highmagnetic moment.

A bevel capping layer may be provided on top of the main pole, via step304. A bottom antireflective coating (BARC) may also be provided on thebevel capping layer, via step 304. The BARC is used to reducereflections during subsequent photolithographic processing. FIG. 7depicts the transducer 400 after step 304 is performed. Thus, anunderlayer 402 and main pole 404 on the underlayer 402 are shown.Proximate to the ABS location, the underlayer 402 may be nonmagnetic.However, distal from the ABS, the main pole 404 may reside on anotherpole, as depicted in FIG. 5. Referring back to FIGS. 6-13, also shownare the bevel capping layer 406 and BARC 408. The bevel capping layer406 is nonmagnetic and may include materials such as aluminum oxide,silicon oxide, a silicon nitride, and/or nonmagnetic metals such as Ru,Ta, and/or Cr. The bevel capping layer 406 may be used to protect thetop of the main pole 404 during subsequent processing steps, such aslift-off and a reactive ion etch (RIE). The bevel capping layer may alsoallow tailoring of the field gradient from the main pole 404. The BARClayer 404 may include materials such as diamond-like carbon (DLC),silicon nitride, and/or an organic antireflective coating. However,other materials might be used for the bevel capping layer 406 and/or theBARC 408.

A mask is provided on the BARC distal from the ABS location, via step308. The mask may be a photoresist mask. Thus, step 308 may includedepositing the photoresist, then patterning the photoresist usingphotolithographic techniques. In other embodiments, the mask may be ahard mask such as DLC or aluminum oxide. In such embodiments, the hardmask is patterned as part of step 308. FIG. 8 depicts the transducer 400after step 308 is performed. Thus, the mask 410 has been provided. Ascan be seen in FIG. 8, a portion of the main pole 404, bevel cappinglayer 406, and BARC 408 proximate to the ABS location are exposed by themask 410. The height and distance of the mask 410 from the ABS locationare desired to be determined based upon characteristics of the bevel tobe formed. More specifically, the mask 410 is desired not to adverselyaffect the ion mill of step 310, discussed below.

After the mask is provided, a high energy ion mill is performed at anangle from a normal to the top of the main pole, via step 310. In someembodiments, the high energy ion mill is at an energy of at least fivehundred eV. In other embodiments, the high energy ion mill is at anenergy of at least seven hundred eV. FIG. 9 depicts the transducer 400during step 310. The high energy ion mill is performed at an angle, α,from normal to the top surface of the main pole 404. The angle α is atleast thirty-five degrees and not more than fifty-five degrees. In someembodiments, the angle α is at least forty and not more than fiftydegrees. This high energy ion mill is a backside ion mill. Thus, theangle α is such that the ions approach the ABS from the back side of thetransducer 400, distal from the ABS. Also shown in FIG. 9 is a frontside ion mill that may optionally be performed as part of the highenergy ion mill. The front and back side ion mills may be interspersedso that the high energy ion mill of step 310 is a combination of one ormore front and back side ion mills. The front side ion mills may be atthe same energy as the back side ion mill, but may be carried out foronly a small portion of the time. The front side ion mills may be usedto remove redeposition on from the ion mill. As can be seen in FIG. 9, aportion of the top of the main pole 404, a portion of the BARC 408, anda portion of the bevel capping layer 406 proximate to the ABS areremoved. In addition, a portion of the mask 410 is also consumed. Insome embodiments, all of the mask 410 may be removed during the ionmilling of step 310. It is believed that consumption of the mask 410 maybe desirable because a more level bevel surface 412 may be achieved.However, consumption of the mask 410 is not required. The high energyion mill of step 310 also exposes a top bevel surface 412 of the mainpole 404. The top bevel surface 412 and corresponding bevel are bothdenoted by the numeral 412. Also shown in FIG. 9 is the damaged region414 due to the high energy ion mill. In general, the damaged region 414is amorphous and at least twenty-six Angstroms thick.

Any remaining portion of the mask 410 is removed after the high energyion mill, via step 312. Step 312 may also include removing the BARClayer. For example, a lift-off may be performed for the mask 410 andBARC 408. In addition, an oxygen RIE and Eco-snow process may beperformed to remove any fencing (not shown). In such embodiments,additional damage may be done to the bevel surface 412. For example, insome embodiments, the thickness of the damaged region may increase tothirty eight through forty-three Angstroms. FIG. 10 depicts thetransducer after step 312 is performed. Thus, the bevel cap 406 isexposed. In addition, although shown as unchanged, the damaged region414 may be thicker.

A low energy ion mill is performed at an energy lower than the highenergy ion mill and at a glancing angle from the top bevel surface 412,via step 314. The energy of the low energy ion mill may be at leastthree hundred eV less than the energy of the high energy ion mill. Insome embodiments, the energy is less than or equal to two hundred andfifty eV. In other embodiments, the energy does not exceed two hundredeV. In some such embodiments, the energy is not more than one hundredeV. FIG. 11 depicts the transducer 400 during the low energy ion mill ofstep 314. The low energy ion mill is performed at a glancing angle, β,from the bevel surface 412. In some embodiments, β is at least ten andnot more than fifteen degrees. Further, as can be seen in FIG. 11, thelow energy ion mill is a back side ion mill. A substantial portion ofthe damaged region 414 may be removed. For example, in some embodiments,the thickness of the damaged region 414 after step 314 may be on theorder of nineteen through twenty-one Angstroms. In some embodiments, thethickness of the damaged region 414 is less than twenty Angstroms afterthe low energy ion mill of step 314.

A nonmagnetic gap is provided, via step 316. Step 316 generally includesperforming a preclean, such as a sputter etch. Once the preclean isperformed, nonmagnetic, write gap may then be deposited. The nonmagneticgap may be insulating or conductive. For example, the nonmagnetic gapmay include aluminum oxide and may be deposited via ALD. FIG. 12 depictsthe transducer 400 after step 316. In addition to preparing the surfacefor the nonmagnetic gap, the preclean has removed some additional damagedue to the high energy ion mill and possibly other processing. In someembodiments, the damaged region 414 is not more than twenty Angstromsthick. In other embodiments, the damaged region 414 may be not more thanfifteen Angstroms thick after step 316. Further, nonmagnetic gap 412 hasbeen provided.

A wrap-around shield may also be provided, via step 318. Step 318 mayinclude a preclean and deposition of seed layer(s) for the wrap-aroundshield. The wrap-around shield may be electroplated or deposited inanother manner. FIG. 13 depicts the transducer 400 after step 318 isperformed. Consequently, shield 420 is shown. Subsequent processing maythen be performed, via step 320. Thus, insulating layer(s), coils,shields, and/or other features may be fabricated.

Using the method 300, improvements in the performance and manufacturingof the transducer 400 may be achieved. In some embodiments, thethickness of the damaged, amorphous region 414 may not exceed twentyAngstroms in the final device. In some embodiments, the thickness of thedamaged region 414 in the final device is not more than fifteenAngstroms. Because the damaged region 414 is thinner, reductions in thesaturation magnetization of the main pole 404 due to the damaged region414 maybe ameliorated. Such a higher saturation magnetization isgenerally desirable in the main pole 404. Further, the thickness of thenonmagnetic gap layer 406 may be better controlled. Thus, performance ofthe transducer 400 may be improved.

1. A method for fabricating a magnetic recording transducer comprising:providing a main pole having a bottom and a top wider than the bottom;performing a high energy ion mill at an angle from a normal to the topof the main pole and at a first energy, the high energy ion millremoving a portion of the top of the main pole, exposing a top bevelsurface for the main pole; and performing a low energy ion mill atsecond energy and a glancing angle from the top bevel surface, theglancing angle being not more than fifteen degrees, the second energybeing less than the first energy; depositing a nonmagnetic gap.
 2. Themethod of claim 1 further comprising: providing a wrap-around shield onthe nonmagnetic gap.
 3. The method of claim 1 wherein the first energyis at least five hundred electron volts.
 4. The method of claim 3wherein the first energy is at least seven hundred electron volts. 5.The method of claim 1 wherein the second energy is less than two hundredfifty electron volts.
 6. The method of claim 5 wherein the second energyis less than two hundred electron volts.
 7. The method of claim 6wherein the second energy is not more than one hundred electron volts.8. The method of claim 1 wherein the second energy is at least threehundred electron volts less than the first energy.
 9. The method ofclaim 1 wherein the glancing angle is at least ten degrees.
 10. Themethod of claim 1 wherein the angle is at least thirty-five degrees. 11.The method of claim 1 wherein the angle is not more than fifty-fivedegrees.
 12. The method of claim 1 further comprising: providing a maskdistal from an air-bearing surface (ABS) location before performing thehigh angle ion mill.
 13. The method of claim 12 further comprising:removing the mask after performing the high angle ion mill and beforeperforming the low angle ion mill.
 14. A method for fabricating amagnetic recording transducer comprising: providing a main pole having abottom and a top wider than the bottom; providing a bevel capping layeron the top of the main pole, the bevel capping layer being nonmagnetic;providing a bottom antireflective coating (BARC) on the bevel cappinglayer; providing a mask on the BARC distal from an air-bearing surface(ABS) location; performing a high energy ion mill at an angle from anormal to the top of the main pole and at a first energy after the maskis provided, the high energy ion mill removing a portion of the top ofthe main pole proximate to the ABS, a portion of the BARC proximate tothe ABS, and a portion of the bevel capping layer proximate to the ABS,the high energy ion mill exposing a top bevel surface of the main pole,the first energy being greater than seven hundred electron volts, theangle being at least thirty-five degrees and not more than fifty-fivedegrees; removing the mask and the BARC after the high energy ion mill;performing a low energy ion mill at second energy and a glancing anglefrom the top bevel surface, the glancing angle being at least ten andnot more than fifteen degrees, the second energy being less than twohundred electron volts; depositing a nonmagnetic gap; and providing awrap-around shield on the nonmagnetic gap.
 15. A magnetic recordingtransducer having an air-bearing surface (ABS) comprising: a main polehaving a bottom, a top wider than the bottom, and a top bevel proximateto the ABS; an amorphous layer on the top bevel and having a thicknessof less than twenty Angstroms; a nonmagnetic gap, at least a portion ofthe nonmagnetic gap residing on the top bevel; and a wrap-around shieldon the nonmagnetic gap.
 16. The magnetic recording transducer of claim15 wherein the amorphous layer is not more than fifteen Angstroms thick.